The present invention is directed towards an apparatus for causing constriction of the pupils of the eyes of a person, and more particularly to an apparatus for causing constriction of the pupils of the eyes of a person to prevent vision impairment resulting from deformities in the cornea which cause light entering the person's eyes to be improperly refracted by the cornea.
A cross-section of the human eye is illustrated in FIG. 1. The eye has a cornea 10 at the outermost front portion of the eye, an iris 12 which is annular in shape, and a lens 14 disposed adjacent the side of the iris 12 opposite the cornea 10. The iris 12 has a circular opening at its center which is referred to as the pupil 16. The iris 12 is composed of light-sensitive tissue, and its size changes in response to the intensity of light. As a result, the pupil 16 dilates in the presence of relatively weak light and constricts in the presence of relatively strong light. The retina 18 is disposed on the back surface of the eye. Visual images are generated by the eye by detecting light passing through the cornea 10, the pupil 12, and the lens 14 and converting light images falling on the retina 18 to optic signals, which are transmitted to the brain via the optic nerve 20.
A number of people have deformities in the corneas of their eyes which cause vision impairment, particularly at night. Such deformities include naturally occurring deformities, such as an irregular curvature of the cornea around its edges which occurs in the eyes of some myopic people, and artificially caused deformities, such as scar tissue resulting from eye surgery. One type of eye surgery that generates such deformities is a procedure referred to as radial keratotomy (RK). The RK procedure is performed in an attempt to correct the vision of a person to obviate the need to wear eyeglasses. In the RK procedure, a number of radial slits are made in the outer periphery of the cornea to change the curvature of the cornea, and therefore change the effective focal length of the eye.
An undesirable effect of the RK procedure is the formation of scar tissue where the radial slits in the cornea were made. Although the scar tissue does not interfere with vision during the day, it typically results in vision impairment at night, causing a "starburst" effect, which substantially impairs night vision and may cause night blindness.
The inventor realized that the vision impairment caused by the RK procedure generally occurs only at night because the pupils of a person's eyes are larger at night. FIG. 2A is a schematic representation, as it would appear during the daytime, of the eye of a person who has undergone the RK procedure. Referring to FIG. 2A, a plurality of radial deformities resulting from scar tissue are designated with the numeral 22. The deformities 22, which generally correspond in size to the radial slits that were performed during the RK procedure, do not extend sufficiently to reach the pupil 16, which is relatively small because of the generally strong light during the daytime. Because the deformities 22 do not extend over the pupil 16, any light that is improperly refracted by the cornea 10 due to the deformities 22 does not pass through the pupil 16 and therefore does not adversely affect vision.
However, when the pupil 16 dilates due to the relatively weak light generated at night, such as the light intensity that would be encountered while driving at night, the ends of the deformities 22 overlap the pupil 16 as shown in FIG. 2B. As a result, a portion of the light that is improperly refracted by the deformities 22 does pass through the pupil 16 to the retina 18, and thus interferes with the person's vision.
The vision impairment caused by deformities in the cornea has serious consequences, such as the inability to drive at night. Due to the irregular manner in which the corneal deformities affects vision, the vision impairment cannot be remedied by simply wearing corrective lenses. This condition may be treated to some extent by medication which restricts the normal dilation of the pupil. However, such medication has relatively long-term effects and would prevent a person's eyes from readily adapting to light conditions changing over a relatively short period of time.